Power Control of Device-To-Device Synchronization Signal

1. A method of setting a power of a secondary device-to-device synchronization signal, SD2DSS, by a first wireless device to enable a second wireless device to synchronize timing of the second wireless device to a timing derived from the first wireless device, the method comprising: determining power of a primary device to device synchronization signal, PD2DSS, transmitted by the first wireless device; and setting the power of the SD2DSS to be less than the power of the PD2DSS, the SD2DSS being transmitted with a power less than the PD2DSS as determined by a power offset compared to the PD2DSS.

2. The method of claim 1 , wherein the PD2DSS includes a Zadoff-Chu, ZC, sequence and the SD2DSS includes an M sequence.

3. The method of claim 1 , wherein the power of the SD2DSS is the minimum of a nominal value of the power of the PD2DSS and a power threshold.

4. The method of claim 1 , wherein the set power of the SD2DSS is adjusted only when the power of the first signal exceeds a predetermined amount.

5. The method of claim 1 , wherein a same circuitry generates the SD2DSS and a secondary synchronization signal, SSS.

6. The method of claim 1 , wherein the power offset is −4 dB.

7. The method of claim 1 wherein the power offset is determined autonomously by the first wireless device.

8. A wireless device configured to set a power of a secondary device-to-device synchronization signal, SD2DSS, to enable a second wireless device to synchronize timing of the second wireless device to a timing of the wireless device, the wireless device comprising: a processor; and a memory, the memory containing instructions executable by the processor, the instructions when executed configure the processor to: determine power of a primary device to device synchronization signal, PD2DSS transmitted by the wireless device; and set the power of the SD2DSS to be less than the power of the PD2DSS, the power of the SD2DSS being transmitted with a power less than the PD2DSS as determined by a power offset compared to the PD2DSS.

9. The wireless device of claim 8 , wherein the PD2DSS includes a Zadoff-Chu, ZC, sequence and the SD2DSS includes an M sequence.

10. The wireless device of claim 8 , wherein the power of the SD2DSS is a minimum of a nominal value of the power of the PD2DSS and a power threshold.

11. The wireless device of claim 8 , wherein the power offset is determined autonomously by the wireless device.

12. The wireless device of claim 8 , wherein the power offset is one of configurable and predetermined.

13. A wireless device configured to set a power of a secondary device-to-device synchronization signal, SD2DSS, to enable a second wireless device to synchronize timing of the second wireless device to a timing of the wireless device, the wireless device comprising: a signal power determiner module configured to determine power of a primary device to device synchronization signal, PD2DSS; and an SD2DSS power setting module configured to set power of the SD2DSS to be less than the power of the PD2DSS, the power of the SD2DSS being a minimum of a nominal value of the power of the PD2DSS and a power threshold.

14. The wireless device of claim 13 , wherein the PD2DSS includes a Zadoff-Chu, ZC sequence and the SD2DSS includes an M sequence.

15. A method of determining and transmitting one of a power offset and a power threshold to a wireless device, the method comprising: determining at least one of a power offset and a power threshold for setting a power of a secondary device to device synchronization signal, SD2DSS, by a wireless device, the SD2DSS being transmitted with a power less than a primary device to device synchronization signal, PD2DSS, as determined by a power offset compared to the PD2DSS; and transmitting at least one of the power offset and the power threshold to the wireless device.

16. A network node, comprising: a processor; a memory containing instructions that when executed by the processor configure the processor to determine at least one of a power offset and a power threshold for setting a power of secondary device to device synchronization signal, SD2DSS by a wireless device; a communication interface configured to transmit at least one of the power offset and the power threshold to the wireless device, the power of the SD2DSS being transmitted with a power less than a primary device to device synchronization signal, PD2DSS, as determined by the power offset compared to the PD2DSS; and the memory configured to store the at least one of the power offset and the power threshold.

17. A network node, comprising: a power offset determiner module configured to determine a power offset to be used by a wireless device, to set a secondary device to device synchronization signal, SD2DSS; and a power threshold determiner module configured to determine a power threshold to be used by the wireless device to determine whether to set a power of the SD2DSS, the power of the SD2DSS being transmitted with a power less than the PD2DSS as determined by a power offset compared to the PD2DSS.